Methods for forming memory devices

ABSTRACT

A memory device and a method for forming the same are provided. The method includes forming a plurality of gate structures on a substrate, forming a first spacer on opposite sides of the gate structures, filling a dielectric layer between adjacent first spacers, forming a metal silicide layer on the gate structures, conformally forming a spacer material layer over the metal silicide layer, the first spacer layer and the dielectric layer, and performing an etch back process on the spacer material layer to form a second spacer on opposite sides of the metal silicide layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional application of pending U.S. patent application Ser. No. 16/692,186, filed Nov. 22, 2019 and entitled “MEMORY DEVICES AND METHODS FOR FORMING THE SAME”, the entirety of which is incorporated by reference herein.

BACKGROUND Field of the Invention

The present invention relates to semiconductor technology in particular to memory devices and methods for forming the same.

Description of the Related Art

A flash memory is a non-volatile memory with large capacity, high read/write speed, low power consumption and low cost. Since flash memory is non-volatile, data can remain in a flash memory after the flash memory has been powered off. Therefore, flash memory can be used widely.

As semiconductor devices are scaled down, it is becoming increasingly difficult to manufacture memory devices. Unwanted defects may be generated during the manufacturing of memory devices, and such defects may cause damage to the memory devices, affecting performance. Therefore, continuous improvements to the memory devices are required in order to improve the yield.

BRIEF SUMMARY

In some embodiments of the disclosure, a method for forming a memory device is provided. The method includes forming a plurality of gate structures on a substrate and forming a first spacer on opposite sides of the gate structures. The method also includes filling a dielectric layer between adjacent first spacers and forming a metal silicide layer on the gate structures. The method also includes conformally forming a spacer material layer over the metal silicide layer, the first spacer layer and the dielectric layer, and performing an etch back process on the spacer material layer to form a second spacer on opposite sides of the metal silicide layer.

In some embodiments of the disclosure, a memory device is provided. The memory device includes a plurality of gate structures disposed on a substrate and a first spacer disposed on opposite sides of the gate structures. The memory device also includes a dielectric layer disposed between adjacent first spacers, a metal silicide layer disposed on the gate structures, and a second spacer on opposite sides of the metal silicide layer.

A detailed description is given in the following embodiments with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein:

FIGS. 1A-1H show cross sections of various stages of a method for forming a memory device according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following disclosure provides many different embodiments, or examples, for implementing different features of the high-voltage semiconductor device provided. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed.

FIGS. 1A-1H show cross sections of various stages of a method for forming a memory device 100 according to an embodiment of the invention. Additional processes can be provided before, during or after the steps of the embodiment. In different embodiments, some processes can be moved, omitted or replaced. Additional features can be added to the memory device. In different embodiments, some features described below can be moved, omitted or replaced.

First, as shown in FIG. 1A, a substrate 101 is provided, and a dielectric layer 102, a first gate electrode material layer 103, a dielectric layer 104 and a second gate electrode material layer 105 are sequentially formed on the substrate 101. In an embodiment, the substrate 101 is made of silicon or another semiconductor material. Alternatively, the substrate 101 may include another element semiconductor material, such as germanium (Ge). In an embodiment, the substrate 101 may be made of compound semiconductor, such as silicon carbide, gallium nitride, gallium arsenide, indium arsenide or indium phosphide. In an embodiment, the substrate 101 includes silicon-on-insulator (SOI) substrate or another suitable substrate. In an embodiment, the substrate 101 has doped well regions (not shown) and shallow trench isolation (STI) regions within. The doped well regions are electrically isolated from one another by the STI regions.

The dielectric layer 102 serves as a tunneling oxide film of the memory device. In an embodiment, the material of the dielectric layer 102 may be silicon oxide, hafnium oxide, zirconium oxide, aluminum oxide, aluminum hafnium dioxide alloy, silicon hafnium dioxide, silicon hafnium oxynitride, tantalum hafnium oxide, titanium hafnium oxide, zirconium hafnium oxide, or a combination thereof.

The first gate electrode material layer 103 will later serve as a floating gate of the memory device. In an embodiment, the first gate electrode material layer 103 may be formed of amorphous silicon, polysilicon, one or more metals, metal nitride, metal silicide, conductive metal oxide or a combination thereof. Specifically, the above-mentioned metal may comprise Mo, W, Ti, Ta, Pt or Hf, but it is not limited thereto. The above-mentioned metal nitride may comprise MoN, WN, TiN and TaN, but it is not limited thereto. The above-mentioned metal silicide may comprise WSi_(x), but it is not limited thereto. The above-mentioned conductive metal oxide may comprise RuO₂ and indium tin oxide (ITO), but it is not limited thereto.

The dielectric layer 104 serves as an inter-gate dielectric layer of the memory device. In an embodiment, the dielectric layer 104 has an opening 104 a. In an embodiment, the dielectric layer 104 may be oxide-nitride-oxide (ONO) structure, such as silicon oxide-silicon nitride-silicon oxide.

The second gate electrode material layer 105 will later serve as a control gate of the memory device. The second gate electrode material layer 105 fills the opening 104 a of the dielectric layer 104. In an embodiment, the second gate electrode material layer 105 may be formed of amorphous silicon, polysilicon or a combination thereof. In an embodiment, the material of the second gate electrode material layer 105 is the same as that of the first gate electrode material layer 103. In other embodiments, the material of the second gate electrode material layer 105 is different from that of the first gate electrode material layer 103.

Then, as shown in FIG. 1B, the first gate electrode material layer 103, the dielectric layer 104 and the second gate electrode material layer 105 are patterned by a lithography process and an etching process to form memory unit transistors and select gate transistors. Each of the memory unit transistors has a gate structure comprising a first gate electrode 203, a gate dielectric layer 204 and a second gate electrode 205. Each of the select gate transistors has a gate structure comprising a first gate electrode 203, a gate dielectric layer 204′ and a second gate electrode 205. The gate dielectric layer 204′ has an opening 204 a. An opening 106 is between adjacent memory unit transistors. In an embodiment, the etching process may be dry etch process, wet etch process, plasma etching process, reactive ion etching process, another suitable process or a combination thereof.

Then, as shown in FIG. 1C, a spacer 107 is formed on opposite sides of the gate structure. The top surface of the spacer 107 is lower than the top surface of the second gate electrode 205. In an embodiment, the top surface of the spacer 107 is higher than the top surfaces of the gate dielectric layer 204 and the gate dielectric layer 204′. In an embodiment, the material of the spacer 107 may be silicon oxide, silicon nitride, silicon oxynitride, a combination thereof or another suitable insulating material. In an embodiment, the spacer 107 may be formed by a conformal deposition process, a lithography process and an etching process. In an embodiment, the conformal deposition process may be physical vapor deposition (PVD) process, chemical vapor deposition (CVD) process, atomic layer deposition (ALD) process, evaporation, another suitable process or a combination thereof. In an embodiment, the etching process may be dry etch process.

Referring to FIG. 1C, a dielectric layer 108 is filled between adjacent spacers 107. The top surface of the dielectric layer 108 is lower than the top surface of the second gate electrode 205. The spacer 107 and the dielectric layer 108 completely fill the opening 106. In an embodiment, the top surface of the dielectric layer 108 is higher than the top surfaces of the gate dielectric layer 204 and the gate dielectric layer 204′. In an embodiment, the top surface of the dielectric layer 108 is level with the top surface of the spacer 107. In an embodiment, the dielectric layer 108 may be tetraethoxysilane (TEOS), low-k dielectric material or another suitable dielectric material. In an embodiment, the dielectric layer 108 may be formed by a deposition process, a lithography process and an etching process. In an embodiment, the deposition process may be PVD process, CVD process, ALD process, evaporation, another suitable process or a combination thereof. In an embodiment, the etching process may be dry etch process.

Then, as shown in FIG. 1D, a metal layer 109 is formed over the second gate electrode 205, the spacer 107 and the dielectric layer 108. In the embodiment, the metal layer 109 conformally covers the second gate electrode 205, the spacer 107 and the dielectric layer 108. In an embodiment, the metal layer 109 may be Co, Ti or another suitable metal material. In an embodiment, the metal layer 109 may be formed by PVD process, CVD process, ALD process, evaporation, another suitable process or a combination thereof.

Then, referring to FIG. 1E, an annealing process is performed on the metal layer 109 so that the metal layer 109 reacts with the silicon material of the second gate electrode 205 to form a metal silicide layer 110. In an embodiment, the metal silicide layer 110 has residue 110 a. The residue 110 a is on the spacer 107 and the dielectric layer 108. In an embodiment, the metal silicide layer 110 may be a CoSi₂. In an embodiment, the temperature of the annealing process may be in a range between 500° C. and 850° C.

Then, as shown in FIG. 1F, a spacer material layer 111 is conformally formed over the metal silicide layer 110, the spacer 107 and the dielectric layer 108. In an embodiment, the spacer material layer 111 may be silicon oxide, silicon nitride, silicon oxynitride, a combination thereof or another suitable insulating material. In the embodiment, the spacer material layer 111 is silicon nitride. In an embodiment, the material of the spacer material layer 111 is different from that of the spacer 107. In the embodiment, the spacer material layer 111 may be formed by an ALD process, and the temperature of the ALD process is about 550° C. In other embodiments, the spacer material layer 111 may be formed by PVD process, CVD process, evaporation, another suitable process or a combination thereof.

Then, according to an embodiment, a first etch back process is performed to form a spacer 111 a on opposite sides of the metal silicide layer 110. In an embodiment, the first etch back process is dry etch process. In the embodiment, the top surface of the spacer 111 a is higher than the top surface of the metal silicide layer 110. In other words, the spacer 111 a protrudes over the top surface of the metal silicide layer 110. According to an embodiment, the top surface of the spacer 111 a is higher than the top surface of the metal silicide layer 110, so that the sidewalls of the metal silicide layer 110 is better protected by the spacer 111 a. In an embodiment, the metal silicide layer 110 has a height H₁, and the spacer 111 a has a height H₂. The height H₂ is larger than the height H₁. In other embodiments, the top of the spacer 111 a is level with the top of the metal silicide layer 110. In other embodiments, the top of the spacer 111 a is lower than the top of the metal silicide layer 110. In an embodiment, the spacer 111 a is in direct contact with the metal silicide layer 110. In an embodiment, the bottom surface of the spacer 111 a is level with the bottom surface of the metal silicide layer 110.

It should be noted that the residue 110 a is removed during the first etch back process when the metal silicide layer 110 has residue 110 a. Thus, short circuits between adjacent metal silicide layers 110 may be avoided, and the yield of the memory devices is thereby improved. In another embodiment, a second etch back process may be performed after the first etch back process to ensure the residue 110 a is removed. In the embodiment, the first etch back process uses an etchant that includes CF₄ or CHF₃, and the second etch back process uses an etchant that includes HBr or Cl₂.

Then, as shown in FIG. 1H, a dielectric layer 112 is formed on the metal silicide layer 110, the spacer 111 a, the spacer 107 and the dielectric layer 108. In an embodiment, the dielectric layer 112 completely covers the metal silicide layer 110, the spacer 111 a, the spacer 107 and the dielectric layer 108, so that the dielectric layer 112 fills a gap between adjacent spacers 111 a. In an embodiment, the bottom surface of the spacer 111 a is level with the bottom surface of the dielectric layer 112. In an embodiment, the material of the dielectric layer 112 is the same as that of the dielectric layer 108. In an embodiment, the dielectric layer 112 may be formed by a deposition process and a planarization process. The deposition process may be a PVD process, CVD process, ALD process, evaporation, another suitable process or a combination thereof. In an embodiment, the planarization process may be a chemical mechanical polishing (CMP) process.

Then, after the formation of the dielectric layer 112, vias (not shown) and pads (not shown) may be formed through the dielectric layer 112, the dielectric layer 108 and the dielectric layer 102. In the embodiment, the vias and the pads collectively serve as contact electrodes of bit line/source line. In an embodiment, the vias and the pads may be Ag, Cu, Au, Pt, W, Po or another suitable conductive material. In an embodiment, the vias are formed by an etching process, a deposition process and a planarization process. In an embodiment, the pads are formed by a deposition process, a lithography process and an etching process. In an embodiment, after the formation of the vias and the pads, the process of the memory device 100 is accomplished.

The memory devices and methods for forming the same of the invention can be applied to various flash memories such as NOR flash memory, NAND flash memory, 3D flash memory.

In summary, according to an embodiment of the invention, by forming a spacer material layer on a metal silicide layer, and then removing the horizontal portion of the spacer material layer and the residue of the metal silicide layer using an etch back process, a spacer is formed on opposite sides of the metal silicide layer. Short circuits between adjacent metal silicide layers may thereby be avoided, and the yield of the memory devices is thereby improved.

In addition, according to an embodiment of the invention, the top surface of the spacer is higher than the top surface of the metal silicide layer, so that the sidewalls of the metal silicide layer are better protected by the spacer.

The foregoing disclosure outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art will appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the subjoined claims. 

What is claimed is:
 1. A method for forming a memory device, comprising: forming a plurality of gate structures on a substrate; forming first spacers on opposite sides of the gate structures; filling a first dielectric layer between two adjacent first spacers; forming a metal silicide layer on the gate structures; conformally forming a spacer material layer over the metal silicide layer, the first spacers and the first dielectric layer; and performing an etch back process on the spacer material layer to form second spacers on opposite sides of the metal silicide layer.
 2. The method of claim 1, wherein forming the metal silicide layer comprises: forming a metal layer on the gate structures, the first spacers and the first dielectric layer; and performing an annealing process on the metal layer, so that the metal layer reacts with the gate structures to form the metal silicide layer.
 3. The method of claim 1, wherein after forming the metal silicide layer and before the etch back process, the metal silicide layer has residue on the first spacers and the first dielectric layer.
 4. The method of claim 3, wherein the etch back process comprises a first etching process and a second etching process, the first etching process removes a horizontal portion of the spacer material layer to form the second spacers, and the second etching process removes the residue of the metal silicide layer.
 5. The method of claim 4, wherein the first etching process uses an etchant comprising CF₄ or CHF₃, and the second etching process uses an etchant comprising HBr or Cl₂.
 6. The method of claim 1, wherein the etch back process is a dry etch process.
 7. The method of claim 1, wherein an atomic layer deposition process is performed to form the spacer material layer, and a process temperature of the atomic layer deposition process is about 550° C.
 8. The method of claim 1, further comprising forming a second dielectric layer on the metal silicide layer, the first spacers, the second spacers and the first dielectric layer.
 9. The method of claim 8, wherein the second dielectric layer fills a gap between two adjacent second spacers.
 10. The method of claim 8, further comprising forming a third dielectric layer on the substrate before forming the plurality of gate structures.
 11. The method of claim 10, further comprising forming vias and pads through the first dielectric layer, the second dielectric layer, and the third dielectric layer.
 12. The method of claim 1, wherein the second spacers are on a top surface of the first dielectric layer and top surfaces of the first spacers.
 13. The method of claim 1, wherein the metal silicide layer is on top surfaces of the first spacers.
 14. The method of claim 1, wherein top surfaces of the second spacers are higher than a top surface of the metal silicide layer.
 15. The method of claim 1, wherein a top surface of the first dielectric layer is level with top surfaces of the first spacers.
 16. The method of claim 1, wherein the first spacers are formed by a conformal deposition process, a lithography process and an etching process.
 17. The method of claim 1, wherein each of the gate structures comprises a first gate electrode, a gate dielectric layer and a second gate electrode.
 18. The method of claim 17, wherein at least one of the gate dielectric layers comprises an opening.
 19. The method of claim 17, wherein top surfaces of the first spacers are lower than top surfaces of the second gate electrodes and higher than top surfaces of the gate dielectric layers.
 20. The method of claim 17, wherein top surface of the first dielectric layer is lower than top surfaces of the second gate electrodes and higher than top surfaces of the gate dielectric layers. 